1. Field of the Invention
The present invention relates to a polishing apparatus, in particular, to a polishing apparatus for polishing a peripheral chamfered portion of a semiconductor wafer.
2. Description of Related Art
As a polishing apparatus for polishing a peripheral chamfered portion of a semiconductor wafer such as a silicon single crystal wafer, a compound semiconductor wafer or the like (hereinafter, simply referred to a wafer), a polishing apparatus shown in FIG. 9 has been known.
Such a polishing apparatus 10 comprises a rotatable wafer holding member 30 for holding a wafer w rotated by a motor or the like, a pushing member 20 for pushing a tape T on the surface of which abrasive are adhered, against the peripheral chamfered portion of the wafer W to be polished, a supply reel 25 for supplying the tape T with abrasive, and a take-up reel 28 for taking up the used portion of the tape T. In the conventional polishing apparatus 10, the tape T drawn out of the supply reel 25 is pushed against the peripheral chamfered portion of the wafer W by the pushing member 20 and is transferred in a direction approximately perpendicular to the main surface of the wafer W to polish the peripheral chamfered portion of the wafer W by always using fresh surface portion of the tape T. The used portion of the tape T are taken up by the take-up reel 28 continuously. During polishing, the tape T is swung in a small range in a width direction thereof and the wafer W held by the wafer holding member 30 is rotated. In the conventional polishing apparatus 10, the swing of the tape and the rotation of the wafer w give a relative speed of the peripheral chamfered portion of the wafer W to the tape T.
In a polishing treatment using a tape T, the fresh surface take-up speed of the tape T and the relative speed between the peripheral chamfered portion of the wafer W and the tape T in the polishing area are important elements to perform a good polishing. However, in the conventional polishing apparatus 10, although the take-up speed of the tape T can be freely changed and therefore the fresh surface drawing speed of the tape T can be also freely changed, it is difficult to obtain sufficient relative speed between the peripheral chamfered portion of the wafer W and the tape T in the polishing area. Further, because the surface portions of the tape T near both sides is used on only the small swinging thereof, it is difficult to effectively use the whole surface of the tape T. In order to obtain a sufficient relative speed, it is necessary to rotate the wafer w at a high speed. However, according to such a high speed rotation, there are some fear for generation of vibration of the wafer w caused by eccentricity of the wafer to the rotary axis thereof and some fear for excessive polishing of the edge of the orientation flat portion of the wafer W.